1. Field of the Invention
This invention concerns an improvement in metal-on-plastic surfaces, particularly films such as reflector films. More particularly, it provides such films and methods for their production which are characterized by having significantly enhanced adhesion between the metal component and the plastic film.
2. Background Information
Plastic sheets and films having a functional metal layer adhered to them are relatively commonplace today. They find application in products ranging from amusement balloons to high performance protective tapes to reflective windows. In an application favored for materials of the present invention, the functional metal layer is reflective and the metal-on-plastic films serve as highly specular (reflective) films for use in reflectors, particularly reflectors in fluorescent luminaires. While in some of these applications durability and performance are secondary considerations, in many cases product durability, and especially durability over long periods of time, is a critical performance property.
Southwall Technologies, Inc., the assignee of the present invention, has for several years marketed a reflective film product which is made up of a layer of polyester, such as poly(ethyleneterephthalate), coated with a thick (500-2000 .ANG.) layer of sputter-deposited silver. This silver layer may, if desired for durability reasons or to improve handleability, be overcoated with a sputter-deposited metal or alloy such as nichrome, stainless steel, or the like. This product of Southwall Technologies, Inc. is flexible and can be laminated into the curved form of luminaire reflectors. In that application it has found wide acceptance. This product is capable of a very high degree of specularity that can only be achieved, in the case of plated materials, with very expensive precision plating techniques.
One difficulty that crops up with functional metal-on-plastic products of this type is an unpredictable level of adhesion of the metal layer to the plastic. This problem can manifest itself by delamination of the metal from the plastic. This delamination can be accelerated by harsh conditions such as high humidity, high salt content and the like. The delamination can result in a general failure of the product and, if reflectivity is key, a decided loss in this property.
This delamination can show up in several different configurations of metal-on-plastic films. For example, in one application an adhesive is applied to the metal layer and the plastic film plus metal layer is laminated to another surface. (This may occur in the reflector embodiment described above. In this case, the delamination causes the plastic film itself to physically separate from the other surface. This separation of the plastic is the direct result of the metal layer delaminating from the plastic film. In less severe, but often equally troubling cases, the breakdown in plastic-to-metal adhesion results in a breakdown of the consistent metal properties of the thick second film. If the adhesive is applied to the back of the plastic, delamination of the plastic from the other surface may not occur but instead the functional metal layer may come off the plastic.
The present invention seeks to provide improved metal-on-plastic products and methods for their manufacture. These products have improved adhesion between their functional metal layers and their plastic layers. In the case of reflective embodiments, they achieve this improvement without significant degradation of the total specular reflectance of the product.